Arrangement for magnetically affecting objects under investigation in electron microscopes



E. FUCHS 3,259,742 ARRANGEMENT FOR MAGNETICALLY AFFECTING OBJECTS July 5, 1966 UNDER INVESTIGATION IN ELECTRON MICROSCOPES Filed Sept. 5, 1961 5 Sheets-Sheet 1 y 1966 E. FUCHS 3,259,742

ARRANGEMENT FOR MAGNETICALLY AFFECTING OBJECTS UNDER INVESTIGATION IN ELECTRON MICROSCOPES Filed Sept. 5, 1961 5 Sheets-Sheet 2 In ven for: f/ehara FZ/cfis July 5, 1966 r E. FUCHS 3,259,742

ARRANGEMENT FOR MAGNETICALLY AFFECTING OBJECTS UNDER INVESTIGATION IN ELECTRON MICROSCOPES Filed Sept. 5, 1961 3 Sheets-Sheet 6 /n ventor: fke/la/"a s y v z fill, gs.

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United States Patent 3,259,742 ARRANGEMENT FOR MAGNETICALLY AFFECT- ING OBJECTS UNDER INVESTIGATION IN ELECTRON MICROSCOPES Ekkehard Fuchs, Munich, Germany, assignor to Siemens & Halske Aktiengesellschaft, Berlin and Munich, Germany, a corporation of Germany Filed Sept. 5, 1961, Ser. No. 135,989 Claims priority, application Germany, Oct. 17, 1960, S 70,893 Claims. (Cl. 250-495) The invention disclosed herein is concerned with an arrangement for investigating, with the aid of an optical corpuscular ray micro-scope, briefly referred to as electron microscope, magnetic regions contained in thin specimen layers, comprising, dis-posed in the specimen plane, a Helmholtz coil combination having ring-shaped coils the radius of which is substantially equal to the coil spacing, and means for focusing the imaging optics upon a plane outside of the specimen plane.

The magnetic regions to be investigated are known as Weiss regions or districts and represent homogeneously magnetized regions in the material which is being examined. The direction of magnetization fluctuates statistically from region to region, and the material therefore appears in the absence of an exterior magnetic field, exteriorly nonmagnetic. The magnetization of the Weiss regions which are quantitatively identical but statistically distributed as to the directions thereof, are also referred to as spontaneous magnetization.

The magnetization of the Weiss regions by an exterior field resides, in connection with materials which are here of interest, in that the directions of the spontaneous magnetizations are more or less oriented in the direction of the exterior field. A complete orientation is obtained upon saturation.

Until now, only purely qualitative results could be achieved with corpuscular ray optical methods, for example, with defocused imaging of magnetic regions. Such method proceeds from the observation that the partial rays of the total electron beam directed upon the layer which is to be examined, which permeate the different Weiss regions, are deflected in different directions owing to the different directions of the spontaneous mag- Since the Weiss regions are relatively large (several microns), it is possible to make the borders of the regions visible in an electron microscope, by partial overlapping of neighboring partial rays of the beam, provided that the focusing is not effected with respect to the plane of the layer which is being examined, in which the distribution of the electrons is still homogeneous relative to the cross sectional area of the electron beam, but focusing instead to a plane lying in the direction of the electron beam in back thereof. Accordingly, there is effected a defocused imaging so far as the layer is concerned.

The borders of neighboring Weiss regions appear in the electron microscopic image partially as bright and partially as dark lines. Bright lines will appear at places at which an intensity increase occurs owing to the overlapping of the partial rays, while dark lines will appear at places at which the partial rays permeating the neighboring Weiss reg-ions are deflecting in the sense of mutual repulsion owing to the opposite directions of the spontaneous magnetizations of the neighboring regions.

In accordance with the invention, investigations which may be evaluated quantatitively, may be carried out upon arranging in the specimen plane of the microscope a Helmholtz coil combination comprising ring-shaped coils with the coil radius substantially equal to the coil spacing, and focusing the imaging optics to a plane outside of the specimen or object plane.

The Helmholtz coil combination serves to produce, for example, in connection with the investigation of the behavior of the spontaneous magnetization subjected to the action of an exterior field, a homogeneous magnetic field, the direct-ion of which lies just as generally those of the spontaneous magnetization, parallel to the plane of the layer. The magnetic layer which is to be examined is thereby positioned in the homogeneous region of the magnetic field.

The coils may be mounted upon a rotary disk which can be operatively moved by means of a toothed sector and a pinion, the axis of which is suitably carried outwardly of the microscope by a grooved ring bushing, so as to be actuated from the outside. The position of the coils, attained at any time, and therewith the direction of the magnetic field, can be read at a scale which is provided at the rotary disk.

Appropriate known and suitable means may be provided for regulating the intensity of the Helmholtz coils.

The electromagnetic objective is advantageously disposed at a relatively great spacing, approximately 15 centimeters, in back of the object, so as to avoid influencing the magnetic field, in the o-bject plane, by the lens field. However, an electrostatic object lens can be provided in the neighborhood of or in the object plane, which does not exhibit a disturbing magnetic field.

The optics is in the imaging of magnetic structures, set to a plane outside of the object plane. This method of defocused imaging produced a blurred picture of the layer. A gain as far as the image sharpness is concerned, can be achieved, upon operating with a small illumination aperture. A diaphragm of 5 microns can for this purpose be mounted in the illuminating system, thereby obtaining an illumination aperture of approximately 5 times 10 In the case of defocusing of approximately 5 millimeters, it will be possible to resolve image details of 0.5 micron spacing.

The invention will now be described with reference to the accompanying drawings showing in diagrammatic manner an embodiment thereof, in which:

FIG. 1 is an exploded perspective view illustrating the ray path through the optical corpuscular ray devices of a microscope according to the invention;

FIG. 2 illustrates the coil arrangement with schematic presentation of the means for varying the coil currents; and

FIG. 3 schematically illustrates the holding of an object in the homogeneous area of the magnetic field generated by both coils.

The drawings represent the ray path extending through the optical corpuscular ray devices of a microscope according to the invention. Reference K indicates a condenser lens, B an illumination'diaphragm of about 5 microns diameter, H a rotatable Helmholtz coil pair which is operable from the outside with the aid of a pinion and in the homogeneous field space of which is disposed the sample or specimen to be investigated. Reference 0 indicates the objective, K0 a contrast diaphragm, and P a projective. The image is projected upon a photo plate Ph.

Referring to FIGS. 2 and 3, the Helmholtz coil H comprises the two coils 1 and 2, each of which has a coil body 4 which supports the individual windings 3 of the associated coil. Both coils 1 and 2 are arranged with distance therebetween being equal to the radius of the respective coils. The magnetic field is created by the passage of current through the coils, supplied by a DC. source 5, a variable resistance 6 being illustrated in the particular embodiment as connected in series therewith to enable the varying of the current flowing through the coils 1 and 2, such magnetic field being indicated by magnetic lines of force designated by the reference letter a in FIG. 2. A

C) homogeneous magnetic field is thus produced within and between the coils 1 and 2 of the Helmholtz coil combination H, resulting from the parallely extending lines of force illustrated.

As illustrated in FIG. 3, the coils 1 and 2 may be supported by a rotatable disk 7 having a peripheral gear rim 8 engageable with the actuating pinion illustrated in FIG. 1. The disk 7 is provided with a central aperture 9, in which the object carrier 19 is supported for examination. For this purpose, the object cartridge 11, illustrated as inserted into the object table 12, is provided with a tubular extension 13. This assures that the rotation of the disk 7 with both coils 1 and 2 can suitably influence the object located on the carrier 10.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

I claim:

1. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, means for rotating the Helmholtz coil combination about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to the plane outside the specimen plane.

2. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the field of the Helmholtz coils being regulatable as to the intensity thereof, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane.

3. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the field of the Helmholtz coils being regulatable as to the intensity thereof, means for rotating the Helmholtz coil combination about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane.

4. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, means for rotating the Hehnholtz coil combination about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen. plane, the field of the Helmholtz coil combination being oriented parallel to the specimen plane.

5. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the field of the Helmholtz coils being regulatable as to the intensity thereof, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane, the field of the Helmholtz coil combination being oriented parallel to the specimen plane.

6. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the field of the Helmholtz coils being regulatable as to the intensity thereof, means for rotating the Helmholtz coil combination about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane, the field of the Helmholtz coil combination being oriented parallel to the specimen plane.

7. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the Helmholtz coils being mounted upon a rotatable disk provided with a scale, means for rotating said disk to rotate the coils about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane.

8. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the field of the Helmholtz coils being regulatable as to the intensity thereof, the Helmholtz coils being mounted upon a rotatable disk provided with a scale, means for rotating said disk to rotate the coils about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane.

9. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ring-shaped coils the coil radius of which is substantially equal to the coil spacing, the Helmholtz coils being mounted upon a rotatable disk provided with a scale, means for rotating said disk to rotate the coils about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane, the field of the Helmholtz coil combination being oriented parallel to the specimen plane.

10. An arrangement for investigating, with the aid of a corpuscular beam microscope, magnetic regions contained in thin layers, comprising, disposed in the specimen plane, a Helmholtz coil combination consisting of ringshaped coils the coil radius of which is substantially equal to the coil spacing, the field of the Helmholtz coils being regulatable as to the intensity thereof, the Helmholtz coils being mounted upon a rotatable disk provided with a scale, means for rotating said disk to rotate the coils about an axis extending in parallel with the direction of the corpuscular beam, and means for focusing the imaging optics of the microscope to a plane outside the specimen plane, the field of the Helmholtz coil combination being oriented parallel to the specimen plane.

References Cited by the Examiner UNITED STATES PATENTS 2,260,041 10/1941 Mahl et al 250-495 2,887,583 5/1959 Emanuelson 250-49.5 2,973,433 2/1961 Kramer 250 495 3,021,445 2/1962 Wideroe et a1. 250-495 OTHER REFERENCES Determination of Magnetization Distribution in Thin Films Using Electron Microscopy, by H. W. Fuller et al., from the Journal of Applied Physics, volume 31, No. 2, February 1960, pages 238 to 248.

RALPH G. NILSON, Primary Examiner.

W. F. LINDQUIST, Assistant Examiner. 

1. AN ARRANGEMENT FOR INVESTIGATING, WITH THE AID OF A CORPUSCULAR BEAM MICROSCOPE, MAGNETIC REGIONS CONTAINED IN THIN LAYERS, COMPRISING, DISPOSED IN THE SPECIMEN PLANE, A HELMHOLTZ COIL COMBINATION CONSISTING OF RING-SHAPED COILS THE COIL RADIUS OF WHICH IS SUBSTANTIALLY EQUAL TO THE COIL SPACING, MEANS FOR ROTATING THE HELMHOLTZ COIL COM- 